This invention relates to a shim lead assembly with a flexible connector for use in a superconducting magnet to accommodate movement between the pressurized cryogenic vessel and the outer surrounding vacuum vessel.
As is well known, a magnet can be made superconducting by placing it in an extremely cold environment, such as by enclosing it in a cryostat or pressure vessel containing liquid helium or other cryogen. The extreme cold reduces the resistance in the magnetic coils to negligible levels, such that when a power source is initially connected to the coil (for a period, for example, of ten minutes) to introduce a current flow through the coils, the current will continue to flow through the coils due to the negligible coil resistance, even after power is removed, thereby maintaining a magnetic field. Superconducting magnets find wide application, for example, in the field of magnetic resonance imaging (hereinafter called "MRI").
In such equipment, it is necessary to be able to detachably connect a plurality of electrical connections from a power source outside the vacuum vessel, through the vacuum vessel and through the pressurized helium vessel to the superconducting magnet coils positioned within the pressurized vessel. This is accomplished by a shim lead connector assembly which includes piping or a conduit through which the multiple electrical leads pass with detachable connectors at the ends. The electrical connector on the shim lead assembly mates with a matching connector on the helium vessel magnet connector platform. However, in shipping superconducting magnets to installation sites and in moving superconducting magnets utilized in mobile MRI installations which are repeatedly moved for periodic use at various hospitals or other locations, it has been found that the resulting shocks and vibrations cause small, but potentially damaging, movement or vibrations between the pressure vessel and the outer vacuum vessel, which can damage the superconducting magnet assembly electrical connections. It is particularly important to avoid damage to the helium vessel magnet connector which could result in extended shut-down of the equipment for costly removal and replacement of that connector.
Also, the shim lead 0-ring that seals the magnet penetration well from the atmosphere can be worn by such excessive movement of the shim lead tube caused by movement of the magnet relative to the vacuum vessel. This can result in costly removal and replacement of the shim lead assembly since the shim lead assembly must be disassembled in order to replace the O-ring.
Accordingly, it is highly desirable to be able to accommodate vibration or relative movement between the pressure vessel and the surrounding vacuum vessel in the shim lead connector assembly. However, the resultant assembly must be capable of detachable connection from outside the outer vacuum vessel to the pressure vessel, and must be able to withstand the extremely large thermal, electrical and magnetic forces resulting from operation of the superconducting magnet.